1. Field of Invention
The invention pertains to a method for manufacturing filaments from an optically anisotropic spinning solution in which the spinning solution is extruded through a spinneret comprising a spinning field with a plurality of spinning orifices, into a coagulation bath through a slot or diaphragm, the edges thereof being formed by plates with upper and lower sides, the upper sides of the plates being defined as the sides having the shortest distance to the spinning field, and to an air gap spinning device for performing said method.
2. Description of Related Art
Such a method is known from European Patent No. 0,904,431, wherein it has been disclosed that the motion of the coagulant surface can be reduced when the edges of adjacent openings are at different heights (“on different levels”). In the examples of said patent specification, filaments of good strength are made. This method, however, suffers from the disadvantage that the coagulation bath during the spinning procedure is still in continuous movement, which is particularly troublesome when applied on a larger scale. Such movement has a disadvantageous effect on the filaments formed, since the filaments in the coagulation bath will stick together, rendering the end product unsuitable for use in the envisaged high-grade applications (e.g., woven fabrics or composite reinforcement).
When very small air gaps are employed (say, smaller than 4 mm), there is a risk of the coagulant, which will always display some motion under the influence of the filament bundle (vibrations, small waves, etc.), making contact with the spinneret plate. When this happens, the process may be disturbed to such a degree, that it will be required to be stopped. Hence, if very small air gaps are to be used, it is of the essence to have the calmest possible coagulation bath surface. It was found that the extent to which the coagulation bath surface is in motion is highly dependent on the geometry of the coagulation bath's bottom. Particularly, when use is made of more than two spinning fields and a corresponding number of discharge openings in the bottom of the coagulation bath, the extent to which there is motion at the coagulant surface can be reduced substantially by introducing the geometry of the present invention. A very simple and effective embodiment that provides a substantial improvement of the known method is the one of the present invention.